Around 1 in 7 gay and bisexual men cured of hepatitis C at major treatment centers in Germany have become reinfected since 2014, according to findings from the German Hepatitis C Cohort presented at the 16th European AIDS Conference (EACS 2017) in Milan in October. At least half of these men became reinfected within a year of completing treatment and all reinfections occurred within 18 months.

The risk of hepatitis C virus (HCV) reinfection is thought to be highest among men who share drug injecting equipment during sex -- known as chemsex -- but Stefan Mauss of the Center for HIV and Hepatogastroenterology in Dusseldorf said that sharing injecting equipment during sex might explain only a quarter of these cases of reinfection.

People infected with HCV who are cured of the infection are vulnerable to reinfection. Although a proportion of people will clear hepatitis C spontaneously, it is not clear if a successful response to previous treatment increases the likelihood of clearing a subsequent HCV infection.

Several studies with varying periods of follow-up have looked at the risk of reinfection among men who have sex with men in Europe.

A study in London carried out prior to the introduction of direct-acting antiviral treatment found reinfection incidence of 9.6 cases per 100 person-years of follow-up. More recently, a multicenter study in western and central Europe found an incidence of reinfection of 7.3 per 100 person-years. The study also found big variations between cities.

The German Hepatitis C Cohort collects information on everyone treated with direct-acting antivirals at 9 treatment centers in Germany. In this analysis, investigators reviewed reinfection rates among 1533 people who had been cured of hepatitis C and compared rates of reinfection according to potential risk factors.

A total of 32 cases of reinfection were identified, all in men. Of these, 5 cases occurred among men who injected drugs (an incidence of 0.96%) and 27 cases occurred among men who have sex with men (an incidence of 13.1%). Only 7 of the men who have sex with men said that they had used injection drugs, suggesting either a discomfort about disclosing drug use or predominantly sexual transmission.

Reinfection occurred fairly soon after completing treatment, within a median of 53 weeks (range 36-70 weeks). In almost half of cases (44%) the reinfection was with a different HCV genotype.

A study of acute HCV infections at one of London's largest sexual health and HIV clinics, the Mortimer Market Clinic, found that among 95 people diagnosed with acute HCV infection between 2015 and 2017, 27% reported condomless anal intercourse as their only risk factor. Almost all those acutely infected with HCV were men who have sex with men (94%) and only 27% reported injecting drugs.

Almost a quarter of the infections (22 cases) occurred in people who were HIV-negative, leading presenter Emily Chung to recommend that risk-based screening for HCV infection should now be considered for HIV-negative men who have sex with men, as well as those who are HIV-positive.